Comprehensive Pediatric Cardiology and Congenital Heart Disease Notes`Bank Notes集 Cardiology Study Notes Q Notes & Study NOTES

Cardiac Anatomy and Fetal Physiology

• Right Atrium Drainage: The coronary sinus, which collects venous blood from the myocardium, drains directly into the right atrium. The sinoatrial (SA) node is situated in the right atrium near the superior vena cava, where it initiates the cardiac impulse.

• Ductus Venosus: In fetal circulation, the ductus venosus shunts oxygenated blood from the umbilical vein directly into the inferior vena cava (IVC).

• Umbilical Cord Composition: The umbilical cord contains two umbilical arteries carrying deoxygenated blood from the fetus to the placenta and one umbilical vein carrying oxygenated blood back to the fetus.

• Fetal Hemoglobin ($HbF$): $HbF$ has a higher affinity for oxygen than adult hemoglobin ($HbA$). Its oxyhemoglobin dissociation curve is shifted to the left compared to adult hemoglobin, facilitating the transfer of oxygen from the mother to the fetus across the placenta.

Transitional Circulation at Birth

• Pulmonary Resistance and Blood Flow: At birth, the first breaths expand the lungs, causing a sharp decrease in pulmonary vascular resistance ($PVR$) and a rise in systemic vascular resistance ($SVR$). Modern oxygen levels cause vasodilation of pulmonary vessels, leading to a marked increase in pulmonary blood flow.

• Cardiac Pressure Changes: Removal of the placenta and lung expansion increase the blood return to the left atrium, raising its pressure above the right atrium pressure. This pressure reversal causes the functional closure of the foramen ovale.

• Pulmonary Fluid Clearance: A surge of catecholamines at birth activates sodium channels in the pulmonary epithelium, assisting in the reabsorption of alveolar fluid to clear the lungs for air breathing.

• Closure of the Ductus Arteriosus: The rise in arterial oxygen tension ($PaO_2$) post-birth triggers the constriction of the ductus arteriosus, typically achieving functional closure within hours. Its patency in the fetus is maintained by the vasodilating effects of Prostaglandin $E_2$ ($PGE_2$).

Cardiovascular Physical Signs and Jugular Venous Pulse

• Jugular Venous Pulse ($JVP$):

  • The 'y' descent represents the rapid emptying of the right atrium into the right ventricle immediately after the tricuspid valve opens in early diastole.

• Blood Pressure Dynamics: Diastolic blood pressure depends primarily on systemic vascular resistance ($SVR$). Conditions causing peripheral vasoconstriction, such as decreased body temperature (to conserve heat) or acute hypoxia, increase diastolic BP. Conversely, Patent Ductus Arteriosus ($PDA$) lowers diastolic pressure due to diastolic runoff.

• Cardiac Pulses:

  • Bounding Pulse: Associated with $PDA$ due to wide pulse pressure.

  • Radio-femoral Delay: A hallmark of Coarctation of the Aorta.

  • Impalpable Femoral Pulses: Suggestive of critical coarctation of the aorta or Hypoplastic Left Heart Syndrome ($HLHS$).

• Murmur Characteristics:

  • Pansystolic Murmur: Heard in Ventricular Septal Defect ($VSD$) and Atrioventricular Septal Defect ($AVSD$).

  • Ejection Systolic Murmur: Common in Aortic Stenosis ($AS$), Pulmonary Stenosis ($PS$), and Tetralogy of Fallot ($TOF$) due to right ventricular outflow tract obstruction ($RVOTO$).

  • Continuous Machinery Murmur: Characteristic of $PDA$, heard at the left upper sternal edge.

  • Fixed Split $S_2$: The classic finding for Atrial Septal Defect ($ASD$) due to right-side volume overload delaying pulmonary valve closure.

Electrocardiography (ECG) and Cardiac Electrophysiology

• Component Definitions:

  • P Wave: Represents atrial depolarization.

  • PR Interval: Represents the time from the start of atrial depolarization to the start of ventricular depolarization. It is the best measure of atrioventricular ($AV$) node conduction time.

  • QRS Complex: Represents ventricular depolarization.

  • T Wave: Represents ventricular repolarization. Its onset correlates with the start of ventricular relaxation (diastole).

  • ST Segment: Represents the plateau phase of ventricular depolarization.

• Calculations: The corrected QT interval ($QTc$) is calculated using Bazett’s formula: $QTc = \frac{QT}{\sqrt{RR}}$.

• Diagnostic Findings:

  • Dominant R wave in V1: Indicates Right Ventricular Hypertrophy ($RVH$).

  • Superior QRS Axis ($240^\circ \text{ to } 380^\circ$): Highly suggestive of $AVSD$ and is common in Down Syndrome.

  • Delta Wave: A slurred upstroke of the QRS complex with a short PR interval, diagnostic of Wolff-Parkinson-White ($WPW$) syndrome.

  • Tall Peaked T Waves: An early sign of hyperkalemia (K^+ > 5.5\,mmol/dm^3).

  • Inverted T Waves in V6: Suggestive of severe left ventricular cardiomyopathy.

Congenital Channelopathies

• Long QT Syndrome ($LQTS$):

  • Congenital abnormalities of potassium or sodium channels (e.g., $KCNQ1$ gene mutations in $LQT1$) cause delayed repolarization.

  • Triggers for syncope include exercise/exertion (common in $LQT1$), sudden noise/early morning alarms ($LQT2$), or sleep ($LQT3$).

  • Romano-Ward Syndrome: Inherited $LQTS$ with normal hearing.

  • Jervell and Lange-Nielsen Syndrome: Inherited $LQTS$ associated with sensorineural deafness.

  • Contraindicated Drugs: Macrolides like Erythromycin and Clarithromycin must be avoided as they further prolong the QT interval.

• Brugada Syndrome: Another primary channelopathy predisposing to ventricular arrhythmias.

Congenital Heart Diseases (CHD)

• Acyanotic Lesions (Left-to-Right Shunts):

  • Ventricular Septal Defect ($VSD$): The most common $CHD$. Perimembranous is the most common subtype. Heart failure degree is best predicted by the Pulmonary:Aortic flow ratio ($Q_p:Q_a$). Moderate $VSDs$ cause dilation of the left atrium and left ventricle. Inlet and outlet $VSDs$ are unlikely to close spontaneously.

  • Atrial Septal Defect ($ASD$): Most commonly the secundum type in the region of the fossa ovalis. Often asymptomatic until later childhood.

  • Patent Ductus Arteriosus ($PDA$): Large shunts cause fluid retention and dilutional hyponatremia due to Atrial Natriuretic Peptide ($ANP$) release.

• Cyanotic Lesions (Right-to-Left Shunts or Parallel Circulation):

  • Tetralogy of Fallot ($TOF$): Characterized by $RVOTO$, overriding aorta, $VSD$, and $RVH$. Cyanotic spells (tet spells) occur due to infundibular spasm leading to increased right-to-left shunting. Radiograph shows oligemic (decreased) lung fields.

  • Transposition of the Great Arteries ($TGA$): Results from failure of the conotruncal septum to spiral. Systemic and pulmonary circulations run in parallel. Presents with severe early cyanosis and plethoric (increased) lung fields.

  • Total Anomalous Pulmonary Venous Return ($TAPVR$): Pulmonary veins drain into the right atrium. Supracardiac types show a "snowman" or "figure-of-eight" sign on X-ray.

• Obstructive and Duct-Dependent Lesions:

  • Coarctation of the Aorta: Narrowing of the descending aorta, often distal to the left subclavian artery. Signs include hypertension in upper limbs and weak pulses in lower limbs. Inferior rib notching (3rd, 4th, 5th ribs) may be seen in older children.

  • Hypoplastic Left Heart Syndrome ($HLHS$): Systemic circulation collapses once the ductus closes, leading to shock and weak pulses throughout.

  • Duct-Dependent Pulmonary Flow: Conditions like Pulmonary Atresia or severe Pulmonary Stenosis require Prostaglandin $E_1$ to maintain oxygenation.

Inflammatory and Acquired Conditions

• Kawasaki Disease: A systemic vasculitis. Diagnosis requires $\ge 5$ days of fever plus 4 of 5 criteria: bilateral non-purulent conjunctivitis, oral mucosal changes (strawberry tongue/red lips), polymorphous rash, peripheral extremity changes (oedema/peeling), and cervical lymphadenopathy (> 1.5\,cm). Treatment is high-dose aspirin and intravenous immunoglobulin ($IVIG$).

• Rheumatic Fever: Caused by an autoimmune response to Group A $\beta$-hemolytic streptococcus. Diagnosis follows Jones Criteria (2 Major or 1 Major + 2 Minor). Major criteria include Migratory Polyarthritis, Carditis, Subcutaneous Nodules, Erythema Marginatum, and Sydenham’s Chorea. Treatment is penicillin and anti-inflammatory agents.

• Infective Endocarditis: Diagnosed with at least 3 sets of blood cultures. Symptoms include fever, night sweats, and lethargy. Splenomegaly and microscopic hematuria may be present.

• Dilated Cardiomyopathy: Frequently caused by Enterovirus infection. Can also be caused by chronic atrial tachycardia.

Cardiac Pharmacology

• Vasoactive Agents:

  • Noradrenaline: A potent vasoconstrictor acting on $\alpha_1$-adrenergic receptors.

  • Dobutamine: A $\beta_1$ and $\beta_2$ agonist used to increase myocardial contractility and stroke volume.

  • Adenosine: The drug of choice for Supraventricular Tachycardia ($SVT$); it transiently blocks the $AV$ node to stop re-entry circuits.

  • Milrinone: A phosphodiesterase-3 inhibitor that acts as an inotrope and lusitrope (improves myocardial relaxation).

• Pulmonary Hypertension Medications:

  • Sildenafil: A phosphodiesterase-5 inhibitor that elevates $cGMP$, causing vasodilation.

  • Bosentan: An endothelin-1 receptor antagonist.

  • Nitric Oxide: Increases $cGMP$ to induce local vasodilation.

• Other Medications:

  • Captopril (ACE Inhibitor): Reduces preload and afterload. Side effects include renal failure and teratogenicity (avoid in pregnancy).

  • Prostaglandin $E_1$ ($PGE_1$): Used to maintain patency of the ductus arteriosus in duct-dependent lesions. Can cause apnea as a side effect.

  • Calcium Gluconate ($10\%$): The immediate first step to stabilize cardiac membranes in severe hyperkalemia ($K^+ = 8\,mmol/dm^3$).

Surgical Procedures

• Norwood Operation: Initial surgical management for $HLHS$.

• Arterial Switch Operation: Definitive correction for $TGA$.

• Fontan Operation: Definitive palliation for Tricuspid Atresia, directing systemic venous blood directly to pulmonary arteries.

• Blalock-Taussig ($BT$) Shunt: Palliative procedure for increasing pulmonary blood flow in $TOF$.

• Pulmonary Artery Band: Used palliatively for large $VSDs$ that cannot yet be closed surgically to prevent pulmonary overcirculation.

Questions & Discussion

Case: Collapse in Severe Malnutrition

• Scenario: A 14-year-old girl with BMI < 13.5, $BP = 80/55\,mmHg$, and $HR = 45\,bpm$.

• Diagnosis: Long QT Syndrome. Electrolyte disturbances from malnutrition prolong the QT interval, leading to bradycardia and hypotensive collapse.

Case: Post-Drowning Resuscitation

• Scenario: A 4-year-old found in a pond with ventricular fibrillation.

• Treatment: Immediate Defibrillation at $4\,J/kg$. If a pulse were present with ventricular tachycardia, synchronized DC cardioversion at $0.5\text{--}2.0\,J/kg$ would be used instead.

Case: Persistent Shock despite Fluid Bolus

• Scenario: A 2-year-old with sepsis receives two $20\,mL/kg$ saline boluses. HR remains high ($200/min$) and CRT remains prolonged ($3\,s$).

• Explanation: Poor myocardial contractility. Failure to respond to adequate fluid volume suggests fluid-refractory cardiogenic shock rather than simple hypovolemia.

Discussion: Prophylactic Antibiotics

• Guidance: Prophylactic antibiotics for dental work are generally not recommended for simple defects like $ASD$ or $AS$ unless there is a prosthetic valve or unrepaired cyanotic heart disease.